My son who is now 6 only weighs about 40 pounds. And he can where some 2t clothes. He has had problems with his weight since he has been born. When we came home from the hospital he was 5.5  and he just hit the 50 percentile on his 6th birthday. He has had feeding tubes put in and everthing. He has been small but his real dad and i are small so i kinda think that might have something to do with it as well. But I have noticed that he is starting to gets these little like pimples on his face and arms. But he is very active and he loves to play ball and basketball. It was funny the other day at his t-ball practice this lady said wow your son can really throw and hit the ball well and I said thank-you. Your son does well also. And then this other lady was commenting on my son and i know her and i said yeah its probably the steroids he is on and the one lady that was talking to me earlier just turned  and looked at me like what the he-- you give your son steroids?? It was so funny it was kinda one of those you had to be there moments. But i did tell her why. But any ways im sure that some children will be small while others will be a bit bigger in size. That is what makes the world go round i guess. LOL